The present invention relates generally to force limiters, and, more particularly, to an improved force-limiting rotary lock that is particularly adapted to be utilized on an aircraft between a driving shaft and one or more airfoil surfaces, such as flaps, slats and the like.
In fixed wing aircraft, flaps are used to redefine the contour of the wing during takeoff and landing. In some cases, a ball screw actuator is used to drive a rotary shaft that controls movement of a plurality of individual flaps that are spaced along the wing. It is generally desirable to provide a force limiter to prevent damage to the actuator structure in the event that an overload condition is sensed.
Various types of rotary locking mechanisms are shown and described in U.S. patent application Ser. No. 09/778,600, filed Feb. 7, 2001, (now U.S. Pat. No. 6,467,363) which is assigned to the assignee of the present application, and in U.S. Pat. Nos. 6,109,415, 4,697,672, 4,579,201, 3,898,817 and 5,582,390. The aggregate disclosures of this application and these patents are hereby incorporated by reference.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention provides an improved force-limiting rotary lock (20) for a shaft (21) mounted in a housing (22) for rotational movement about an axis (x-x). The shaft is also axially movable relative to the housing, and is biased (via Belleville spring stacks 33, 34) to move toward a predetermined axial position relative to the housing. The improved rotary lock broadly comprises: at least one member (28) provided on one of the shaft and housing; a pawl (51) mounted on the other of the shaft and housing, the pawl being movable relative to the member (28) between first and second positions: wherein the pawl is operatively arranged to engage the member when the pawl is in the first position (e.g., as shown in FIG. 3) to prevent further rotation of the shaft in one angular direction, and is operatively arranged to be disengaged from the member when the pawl is in the second position (e.g., as shown in FIG. 2) to permit rotation of the shaft in either angular direction; a cam (25) mounted on one of the shaft and housing; a follower (49) associated with the pawl for selectively moving the pawl between the first and second positions, and operatively arranged to engage the cam when the shaft is axially displaced from the predetermined position such that when the shaft is axially displaced from the predetermined position and the pawl (51) engages the member (28), the shaft will be prevented from rotating further in the one angular direction.
In the illustrated embodiment, each member (28) is a lug or dog that extends outwardly from the shaft. However, in an alternative arrangement, such members (be they dogs, lugs or otherwise) could be mounted on the housing.
Also, in the preferred embodiment, the device is shown as having a single pawl (51) which is operatively mounted for selective movement between any one of three spring-biased positions: a first position (e.g., as shown in FIG. 3) in which the pawl (51) engages a member (28) to prevent rotation of the shaft in one angular direction, a second position (e.g., as shown in FIG. 2) in which the pawl is disengaged from such member and permits rotation of the shaft in either angular direction, and a third position in which the pawl engages a member (28) and prevents further rotation in the opposite angular direction. However, in an alternative embodiment, multiple pawls could be provided.
When the shaft is prevented from rotating in one angular direction, the shaft is not prevented from rotating in the opposite angular direction. Moreover, when the shaft is prevented from rotating in the one angular direction, the pawl is retained in its position independently of the axial position of the shaft. When the pawl is in its first or locked position (i.e., to prevent further rotation in the one angular direction), and the shaft is rotated in the opposite angular direction, even when the shaft is not axially displaced, the pawl will be moved from its locked or first position to its unlocked or second position.
Accordingly, the general object of the invention is to provide an improved force-limiting rotary lock.
Another object is to provide a force-limiting rotary lock for use in controlling airfoil surfaces, such as flaps, slats and the like.